Poly(hydroxyalkanoic acid) (PHA) polymers such as poly(lactic acid) (PLA) can be polymerized from renewable sources rather than petroleum and are compostable. They have a broad range of industrial and biomedical applications as films. For example, JP patent application H9-316310 discloses a poly(lactic acid) resin composition comprising PLA and modified olefin compounds. Examples of those modified olefin compounds are ethylene-glycidyl methacrylate copolymers grafted with polystyrene, poly(dimethyl methacrylate), etc., and copolymers of ethylene and alpha-olefins grafted with maleic anhydride and maleimide. Toughened PHA compositions are also disclosed in, for example, US patent application 2005/0131120 and 2006/0142505; U.S. Pat. Nos. 5,883,199, 6,323,308, 6,417,294, 6,713,175, 6,756,331, 6,960,374, and 7,078,368; and EP0980894 A1 and EP093583B1.
However, physical limitations such as brittleness prevent easy sheet casting and subsequent trimming of the sheet into thermoformed articles. In addition to the difficulties of managing the brittle sheet through the sheet making process, articles subsequently thermoformed from the sheet may lack sufficient toughness for many applications. Some toughened PHA compositions have undesirably poor clarity. Accordingly, it is desirable to obtain a toughened composition to be easily melt-processed into a variety of articles with good toughness, preferably while maintaining acceptable clarity.